The present invention relates to zero adjustment in an electronic timepiece such as an electronic digital wristwatch.
The conventional zero adjustment in a mechanical timepiece was performed in the following manner. When the operator depressed a zero adjustment switch at a time when the second-hand was in a region between 0 and 30, the second-hand was forced to rotate fast in a counterclockwise direction to reach the zero second position. When the operator depressed the zero adjustment switch at a time when the second-hand was in a region between 30 and 60, the second-hand was forced to rotate fast in a clockwise direction to reach the zero second position.
Recently, the above-mentioned zero adjustment technique has been applied to an electronic timepiece. An electronic timepiece employing a quartz oscillator has, generally, high accuracy, and the error in a month can be controlled within 15 seconds. Therefore, when the operator performs the zero adjustment once a week with reference to the time tone, the error of the electronic timepiece can be always maintained below several seconds.
The conventional zero adjustment in an electronic timepiece was achieved in a same manner as for the mechanical one. When the second information was in a region between 0 and 30 at a time when a zero adjustment command was generated, a zero adjust control circuit determined that the timepiece was fast and the second information was forced to become zero without changing the minute information. On the contrary, when the second information was in a region between 30 and 60 at a time when the zero adjustment command was generated, the zero adjust control circuit determined that the timepiece was slow and the second information was forced to become zero with an incremental one step of minute calculation.
By the way, in the electronic timepiece which comprises a quartz oscillator of 32,768 KHz and C-MOS circuits, a ratio of tendencies to fast and to slow is not 1:1. Therefore, when the boundary area to increase the minute information is chosen at 30 seconds, there is a considerably great possibility that erroneous time adjustment is achieved. More particularly, increment one is not effected on the minute information at a time when the zero adjustment operation is performed even when the increment is necessary, or the increment operation is performed at a time when it is not required.